Combinatory Categorial Grammar: An Introduction

Combinatory Categorial Grammar (CCG) is a radically lexicalized theory of natural language grammar, in which the lexicon is the only resource for specifying language-specific information such as the order of constructions. Syntactic projection onto the sentences of the language is defined by a small set of combinatory rules that apply
freely, and are common to all languages. It combines descriptive adequacy---that is, applicability to the constructions and interpretations of a wide range of typologically diverse languages---with explanatory adequacy, in the sense of having the fewest degrees of freedom in the theory in terms of expressive power that is known for an adequate theory of linguistic competence.

Because of its theoretical parsimony and strong adequacy, CCG exhibits a particularly close coupling between syntax and semantics, of the kind envisaged in Montague Grammar and its modern variants, from which it differs in according a central role to logical form as the only representatiional level in the theory. The syntactic type and logical form of the bounded constructions are defined strictly lexically, and are projected onto sentences, including the unbounded constructions, entirely through surface composition, by universally available combinatory rules that apply to strictly adjacent non-empty syntactic types, without movement.

Because of its tight coupling of syntax and semantics, CCG has become widely adopted in computational linguistics, particularly for applications in which semantics plays an important role, such as question-answering, textual entailment inference, and
induction of semantic parsers from data consisting of paired sentences and logical forms. It has also been applied to modeling language acquisition from child-directed
utterance. The course seeks to reexamine the significance of CCG as a linguistic theory of grammar.

Motivation for the course.

Despite its adherence to strictly orthodox linguistic principles, CCG is not widely understood within mainstream linguistics. The reason may be that CCG is a revolutionary theory, seeming to require one to abandon long-held beliefs concerning the reality of surface syntactic structure as a representational level, and even the nature of grammatical constituency itself, for the sake of a theory in which all that was linguistically solid melts into air, and logical form is the only representational level.

It is widely acknowledged that there is currently something of a crisis in theoretical linguistics. The ancillary disciplines of computational linguistics and psycholinguistics, and indeed some influential currents within mainstream linguistics itself, seem to
have entirely given up on the idea that formal linguistic theory has anything to tell them about the use of language. It therefore seems timely to look more closely at CCG in comparison with other approaches that have recently been developed, including those
within the Minimalist Program, and to ask whether a synthesis can be achieved that preserves the linguistic insights of all in a form that can reconnect with a broad range of linguistic disciplines.

Outline
1. Requirements for a Theory of Grammar: the problem of long range dependency; The movement theory; alternatives to movement